The subject matter disclosed herein relates to a system method of acquiring three-dimensional coordinates of points on a surface of an object and in particular to a system of method of operating a laser tracker in conjunction with a scanner device to track the position and orientation of the scanner device during operation.
The acquisition of three-dimensional coordinates of an object or an environment is known. Various techniques may be used, such as time-of-flight or triangulation methods for example. A time-of-flight system such as a laser tracker, for example, directs a beam of light such as a laser beam toward the spot to be measured. An absolute distance meter is used to determine the distance from the distance meter to the spot based on length of time it takes the light to travel to the spot and return. By moving the laser beam over the surface of the object, the coordinates of the object surface may be ascertained. Time-of-flight systems have advantages in being accurate, but in some cases may be slower than systems that project a plurality of light spots onto the surface at each instant in time.
A triangulation system such as a scanner in contrast projects either a line of light (e.g. laser line probe) or a pattern of light (e.g. structured light) onto the surface. In the system, a camera is coupled to the projector in a fixed mechanical relationship. The light/pattern emitted from the projector is reflected off of the surface and detected by the camera. Since the camera and projector are arranged in a fixed relationship, the distance to the object may be determined from captured images using trigonometric principles. Triangulation systems provide advantages in quickly acquiring coordinate data over large areas.
In some systems, during the scanning process, the scanner acquires a series of sequential images of the light/pattern reflected off of the object. These images are then registered relative to each other so that the position and orientation of each image relative to the other images is known. Where the scanner is handheld, various techniques have been used to register the images. One common technique uses features in the images to match overlapping areas of adjacent image frames. This technique works well when the object being measured has many features relative to the field of view of the scanner. However, if the object contains a relatively large flat or curved surface, the images may not properly register relative to each other.
Accordingly, while existing coordinate measurement devices are suitable for their intended purposes, the need for improvement remains, particularly in improving the registration of images acquired by a scanner device.